SEOUL, April 25 (Yonhap) -- The results of Wednesday's by-elections, in which three heavyweight candidates won parliamentary seats, may trigger a major reorganization within both the ruling and opposition parties, political experts said.

In the polls which were largely seen as a test of public support for President Park Geun-hye's government which took office two months ago, one independent and two ruling-party candidates split three parliamentary seats up for grabs.

In Seoul's Nowon C district, Ahn Cheol-soo, a software mogul-turned-independent candidate, emerged the winner after defeating rival Huh Joon-young of the ruling Saenuri Party with 60.5 percent of the vote against Huh's 32.8 percent, according to the National Election Commission.

Ahn, the founder of South Korea's largest anti-virus software firm AhnLab, demonstrated huge political influence among young and liberal voters in December's presidential race, although he eventually dropped out to help boost the chances of the main opposition candidate, Moon Jae-in.

With his comeback in politics, Ahn is expected to pose a challenge to the main opposition Democratic United Party (DUP) as it struggles to overcome factional divides and rebuild in the wake of its presidential election defeat.

Media and political experts have long speculated that Ahn could establish his own political party, a move that could redraw the political map of opposition forces.

Even before Wednesday's by-elections, the ruling party questioned the DUP's political legitimacy when it decided not to field a candidate in Nowon C. The move was seen as repayment for Ahn's withdrawal from the presidential race.

Ahn's victory is also expected to have an impact on the DUP ahead of its national convention scheduled for next week. The party plans to elect its new leadership during the May 4 convention.

"The first by-elections under a new government are a chance for the party that lost in the presidential election to make a comeback, but (the DUP) failed to use that opportunity," said Yoon Hee-woong, a senior analyst at the Korea Society Opinion Institute.

"If public confidence continues to be weak for the DUP, while the possibility of deeper intra-party conflicts remains, a (new) rivalry with Ahn would make it more difficult for the party to pull itself together," he said.

For the ruling party, the by-elections worked in its favor.

The elections had been closely watched as a test of public support for the Park government. Her approval ratings dropped in the early weeks of her single, five-year term after a handful of her nominees for senior government posts resigned over allegations of ethical lapses and other problems.

Kim Moo-sung, a former floor leader of the ruling party and close aide to the president, won a parliamentary seat in Yeongdo in the southeastern port city of Busan with 65.7 of the vote against 22.3 percent for his main rival Kim Bi-oh of the DUP.

With most of the votes counted in the Buyeo and Cheongyang constituency in South Chungcheong Province, the ruling party's Lee One-koo beat his DUP rival Hwang In-seok with 77.3 percent of the vote against Hwang's 16.9 percent.

Kim is viewed as a future contender for the ruling party's chairman, given the large role he played in the presidential election campaign last year. There is even speculation that he could have presidential ambitions.

Meanwhile, Lee is expected to extend his political influence in South Chungcheong Province of central South Korea where he has previously served as governor of the province.

Kim will serve his fifth term as a lawmaker while Lee will serve his third term.

"Wouldn't the two lawmakers, who have considerable political influence, bring new dynamic to the ruling party and change relations between the party and the presidential office?" said a two-term lawmaker, asking that he not be identified. "Kim's bid for party leader is just a matter of time."